Weeks called police and began scouring the area. Before long, a neighborhood mother gave her some chilling news.

"Nicole had been playing with her … daughters and said that Nicole had said she was goin' out on a date," said Weeks.

Like millions of teens, Nicole spent a lot of her social time online. So Weeks feared she might have left to see someone she'd met on the internet.

"You must be a bit panicked at this point?" Van Sant asked Weeks.

"Yeah," she replied.

Local News Report: The FBI has now joined regional and state law enforcement in the search. This afternoon they canvassed from neighborhood…

Nicole's disappearance also sent shockwaves through her hometown of Blacksburg, Virginia, the scene of that infamous 2007 mass shooting at Virginia Tech.

Blacksburg Police press conference: This community is known for stepping up and we need them to do that at this time as we pray for the return of a beautiful young girl.

By midday, Blacksburg was stepping up again.

WDBJ News report: More than 1,200 searchers are on a mission to find the 13-year-old.

Volunteers even brought an infrared drone to aid in the search for Nicole.

"I know she wouldn't go nowhere for that many hours without her medicine," said Weeks.

Nicole was born with a damaged liver and needed a transplant before her first birthday. Now a teenager, she still needed her anti-rejection medication every day to survive. Her illness and surgical treatment had left Nicole with scars on her stomach and neck. Weeks says Nicole had emotional scars as well.

"So she was being bullied?" Van Sant asked.

"Yeah. She hated going to school," Weeks replied. "She would always make me write her a note for gym because they would pick on her about her scar."

Weeks says Nicole not only had trouble fitting in, she also had a difficult relationship with her father, David Lovell. He did prison time on a drug charge and he's had other problems with the law.

"She wanted his attention," Weeks said. "She wanted his love."

"I have regrets that I wasn't there. I feel … you know, what did I do wrong, why wasn't I there for her more often," said Lovell.

He'd left Tammy before Nicole was born. The two were never married.

"When you would go to work, was there anyone supervising her?" Van Sant asked Weeks.

"Yeah, my parents," she replied.

"Your parents, did they live at the house?" Van Sant asked.

"Yes."

"So she never went unsupervised?"

"No," said Weeks.

But Nicole was leading an unsupervised life online through the social media apps on her smartphone.

"It's like a loaded gun," said Pamela Casey, a district attorney in Blount County, Ala., who is on a national crusade warning people about the dangers of social media.

"This is the new crime of our time," she said.

Pamela Casey PSA: If you pick up your child's phone and you don't know the password, that's a problem. If you don't know…

Casey began speaking out long beforeNicole Lovell disappeared in Virginia. Her online safety videos have been seen by millions across the country.

Pamela Casey PSA: I can actually go live on Periscope and post updates to you guys… if I can do that live sitting in my office, then your child can do that live in their bedroom.

"Years ago, you had to worry about your kid getting snatched. Parents don't realize that essentially your kid could get snatched -- their life taken by somebody they meet in their own bedroom," said Casey.

By late on the day Nicole Lovell vanished, her parents' hope was fading with the winter light.

"I didn't sleep at all that night, I waited…" said Weeks.

But it would be three days before Nicole's parents had to face the horrifying news that her body had been found.

"Coley had a passion for pandas, music, dancing ... Nicole touched many people throughout her short life," Weeks said at a press conference the day she got the news, referring to Nicole by her nickname. Weeks was quickly was overcome by emotion and left the podium.

Shock and sadness were everywhere, but investigators had gotten a big break. And it came from Nicole Lovell herself. She'd left behind virtual evidence of a real-life murder.

DIGITAL ROADMAP TO MURDER

Nicole's dad, David Lovell, says even before her body was found, investigators had found a solid lead -- she had handwritten the usernames and passwords to all her accounts on her bedroom wall.

FBI computer forensics experts traced Nicole's account information and quickly established that she'd regularly used Kik – a popular chat app attractive to teens, in part, because they can communicate anonymously without their parents knowing.

"When you had her phone, did you ever click on the Kik app just to see what was inside?" Van Sant asked Weeks.

"No," she replied."I just made her delete it, uninstall it."

"Do you believe she reinstalled it?

"Yeah," said Weeks.

So the FBI put in what they call an emergency disclosure request to Kik. They wanted to see Nicole's personal account, and they make a startling discovery. It turns out that in the last two days of her life, she'd been messaging with a person who had a chilling username: "Dr_Tombstone."

Using an IP address provided by Kik, investigators traced the Dr_Tombstone screen name to David Eisenhauser, 18, a freshman engineering student at Virginia Tech.

David Eisenhauer
Jeffrey F. Bill/Baltimore Sun

David Eisenhauer seemed the last person in the world capable of killing a 13-year-old girl. He'd been a high school track star. Former classmate Dorothy Callahan says his brains and charisma were as strong as his strides.

"He was a very celebrated student, he always had straight A's," Callahan said. "And he was sort of cocky, and he was like, 'Yeah I'm David Eisenhauer, I was just on the local news. I'm a big deal.'"

Nicole Lovell's friends on rumors at school

Three days after Nicole went missing, Eisenhauer was picked up by police at his dorm and taken in for questioning. His roommate, Jeremy Basdeo, walked in on the startling aftermath.

"I went to my room and I saw the door open," he said. "And I got turned around by the Virginia State Police and the FBI."

"He put on boots. But it wasn't raining that hard for boots. But, you know, I just let it go. And then -- he came back at 2:00 in the morning," Basdeo continued.

"Did you ever see a knife in the room?" Van Sant asked.

"Yes," he replied. "He usually leaves[s] it on his desk."

"Was it on his desk when the cops showed up?" Van Sant asked.

"No. They couldn't find it," said Basdeo.

Eisenhauer soon admitted to police he'd talked to Nicole outside her house that night. He was arrested and charged with abduction. Eisenhauer's statements led them to another young woman, Natalie Keepers. She was brought in for questioning, too.

Natalie Keepers

What did 19-year-old Natalie Keepers know about what happened to Nicole Lovell? Keepers -- another Virginia Tech freshman and another unlikely person of interest.

"She wanted to study engineering and be like her father who worked for NASA," Mark Jenkins, a former boyfriend, told "48 Hours."

Investigators strongly suspected Keepers was involved. She too was arrested.

David Eisenhauer and Natalie Keepers: A dark duo?

With two people in custody, police made a grisly discovery. Nicole Lovell's nude body was located 90 miles away in North Carolina.

"What kind of wounds were on her body?" Van Sant asked Surry County Sheriff Graham Atkinson.

"She was stabbed… her throat was cut," he replied. "…and then the thoughts turn to, 'who are the animals who could have done something like this to her?'"

District Attorney Pamela Casey said Eisenhauer and Keepers may represent a new kind of predator.

"Sometimes it's usually the people we least expect," Casey warned.

"They could be your next door neighbor," she said. "…they can stay behind their phone and hide behind their phone -- just like your child is doin'."

Casey said criminals often use apps like Kik. Why? Because it's where kids hang out online. In fact, Kik -- a Canadian company -- claims that millions of American teens use their app every month.

"You can be anybody…" said a convicted predator we'll call "Steve."

He should know. "Steve," 38, said he used the Internet to groom kids and spent 10 years in prison for molestation. He told "48 Hours" he now feels a new urge to sound the alarm about anonymous chat apps like Kik.

"Kik … is a predator's paradise," he said.

"Pedophiles, do they go on Kik, pose as a 13, 14, 15-year-old in order to hopefully strike up a relationship with a child?" Van Sant asked.

"Yes, that's quite common on there," "Steve" replied.

"Steve" demonstrated just how easy it is for an adult to use the Kik app to begin a conversation with a child.

We created -- and later deleted -- a Kik account for the demonstration. "Steve" showed how us how the app could be used to target children.

"My message is: 'I'm sad and lonely,'" said "Steve".

After hitting send, it took just 44 seconds for the first response to arrive. Another girl, apparently a teenager, responded less than three minutes later.

"In two days max, I could have her sending me nude pictures," "Steve" said. "Once you make 'em happy, you got their heart, once you got their heart, everything else follows."

Three months had passed since Nicole Lovell's murder. With David Eisenhauer and Natalie Keepers still behind bars, investigators had discovered text messages that led them to the door of Bryce Dustin.

"I almost felt like he was like a little brother, Dustin said of Eisenhauer.

It was on a gaming site that Dustin first chatted with Eisenhauer. And though they never met in person, they began a six-year-long internet friendship.

"David, you know, kept coming back to me for advice on everything," said Dustin.

"What kind of problems would he ask you for advice about?" Van Sant asked.

"Girls was a big one," Dustin replied.

Dustin told "48 Hours" he remembers Eisenhauer talking last winter about a problem he had with one girl in particular, a girl Dustin now believes was Nicole Lovell.

"He told me that he had found out she was underage and that … she wanted to be with him. And that she was going to expose him if he wasn't with her," he recalled.

He said Eisenhauer was worried about being outed in a relationship with an underage girl. So he offered some big brother kind of advice.

"If she wants to be your girlfriend, you know, let her, but don't be the greatest boyfriend, just like don't text her, just ignore her," Dustin advised. "…she'll go away."

Another family was about to have one of their daughters go away as well -- in the car of an online predator in Spokane, Washington.

THE DANGER IS EVERYWHERE

"Her last moments, is what flashes through my mind. That's my nightmare," said Nicole's father, David Lovell.

Lovell says he wishes he had done better in protecting Nicole.

Nicole Lovell and her dad, David

"If it can happen to my family, it can happen to anybody. I mean, flat out anybody," he said.

It can happen to any family, including one in Spokane, Washington, about 2,500 miles away from Virginia. The parents here got a tip that their 15-year-old daughter was being targeted by a 30-year-old man. And what's worse? The two were planning to run away that very night.

"She was gonna leave her iPad, hop in the car … with a man she doesn't really even know," said Detective Elise Robertson.

It was June 7, 2013, when Detective Robertson of the Spokane Police Department's Special Victims Unit got the kind of call cops all over the country have come to expect.

"A father was saying that his daughter was having an Internet relationship with a 30-year-old man and he had just found out…" she said.

"And that's when everything broke loose," said Brandy Syrotchen.

Until that moment, Brandy, and her husband, Branden Syrotchen, seemed to have the quintessential American family. She, teaching at a local church, he studying for a PhD in Psychology. They'd been hands-on parents, raising their sons, Joshua and Josiah, and daughters Ariel and Elizabeth. They shared a love of God, country, sports and each other.

"My parents were pretty strict," said Elizabeth Syrotchen.

Elizabeth Syrotchen

Elizabeth, now over 18, says it wasn't always easy reconciling her upbringing with a growing lust for life.

"I felt like my parents were holding me back from what the average kid gets to experience," she said.

"And how much did your parents monitor your life?" Van Sant asked.

"I would say that they thought that they were monitoring me … they didn't understand that they actually weren't monitoring me," she explained. "They probably had no clue about Kik and those dating sites."

But her parents did become suspicious when Elizabeth, then 15, suddenly started acting strangely.

"She would be going to bed earlier than normal," her father said.

Elizabeth seemed distracted -- less interested in family activities, in church, and even in friends. Her parents took her smartphone away and asked to see her social media accounts. She refused.

They were stunned to learn just how wrong. It all started with a phone call from Elizabeth's best friend's mother … a call that turned their world upside down.

"Elizabeth is dating a 30-year-old …And he plans on coming down and … getting her at 3 o'clock in the morning," said Brandy Syrotchen.

"That very day?" Van Sant asked.

"Yeah. And we're like, "W—what???" Brandy replied.

Elizabeth Syrotchen and Jason Richards, the 30-year-old man the teen met through a chat app

Elizabeth was angry and evasive, but her parents finally got her passwords and soon discovered the truth. She had been communicating with a stranger: a 30-year-old Seattle-area man named Jason.

"Jason Richards says, 'When I see you, baby, I am grabbing you. Pulling you close to me. And holding you tightly,'" Brandy Syrotchen tearfully read aloud from her daughter's correspondence with the man.

The communications show that initially, Elizabeth told Jason she was 18, but later admitted her real age: 15. The Syrotchens were stunned to learn that the pair had already met in person and been intimate. They were even discussing leaving the country. The two had used apps including Facebook and Kik.

"This is playing out in some ways like your own personal family horror film," Van Sant commented to Elizabeth's parents.

"Yeah," they replied.

The horror continued as the Syrotchens realized that within hours, Jason would be driving the 280 miles from Seattle to Spokane to pick up their daughter. They locked Elizabeth in her room with no phone or Internet access and called police.

"What do you do at that moment? You have a 15-year-old girl who's your only witness who's denying everything," the detective said.

Detective Robertson says that without hard evidence of an actual crime, police had to stay on the sidelines.

"So there's nothing they can do for you?" Van Sant asked the Syrotchens.

"There's absolutely nothing they can do for me," Branden replied.

"And when you hear that you feel totally helpless. And it's, like, 'OK, well, what are you gonna do now?'" said Brandy.

What they did was hatch their own plan to turn the tables on the man who was about to lure their daughter away.

"This is my daughter and nobody's gonna mess with her and nobody's gonna get her. And I'm gonna do what it takes," said Brandy.

Jason had already messaged from the car.

"I needed to communicate with him to get him to our house," Brandy explained.

Brandy and Branden Syrotchen hatched a plan to turn the tables on the man who was about to lure their teenage daughter, Elizabeth, away

Gritting her teeth, Brandy Syrotchen went online -- impersonating her own daughter.

"For seven hours, I sat there and listened to him, 'Oh baby I can't wait to see you … I can't wait to get you in my arms …lay in the same bed together, wake up in the morning,'" she said in tears. "And for seven hours I communicated back, 'Oh baby, I love you too …I can't wait.'"

"In the pit of your stomach that must have made you …" Van Sant began.

Branden recalled that Brandy kept the conversation with Jason Richards going, in the alley behind the Syrotchen's house, he and his friends had set up a sting operation like something out of an action movie.

As Branden waited in his car on one side of the alley getting updates from his wife on the phone, his friend, Damon, waited in his car on the other side of the street.

"So the idea is like a pincer, right, you're gonna trap. It's like a bear trap that's gonna close," said Van Sant.

"Yes," Branden affirmed.

Branden's friend, Phil, brought his 12-gauge shotgun. He'd been trained in Special Forces and had no idea how Jason would react.

TURNING THE TABLES

It was 3 a.m. in Spokane, Washington, but could just as easily been high noon.

As Branden Syrotchen and his team lay in wait, headlights appeared at one end of the alley. A 30-year-old man's sexual road trip to take a 15-year-old girl from her family was about to come to a shocking end.

"He pulls in. At this time, we go ahead and we call Damon down here. And Damon-- just books it," Branden explained. "I'm pulling in here … Jason pulls in right there."

"I said …'Driver … Put your hands on the steering wheel. Do not move or I will shoot you. …Couple of times he moved his hands and I said, 'What part of do not move do you not understand?'" Phil demonstrated.

"If Jason makes some sort of move, are you prepared to pull that trigger?" Van Sant asked.

"If he exited the car abruptly, I would've shot him," Phil replied.

They called police, who arrived minutes later and arrested Jason. In his SUV, they found cell phones and a pair of hunting knives. They would later discover he also owned a handgun.

Detective Robertson learned Jason was actually Jason Richards, a 30-year-old, divorced coffee distributer from the Seattle area. Like David Eisenhauer and Natalie Keepers in the Lovell case, Jason Richards seemed nice and successful on the surface.

"Who is this guy?" Van Sant asked the detective.

"Jason is the guy next door," she replied.

He tried to turn his crime into a love story:

Jason Richards: I pretty much fell for her very quickly … we said "I love you" pretty quickly, about a week and a half into really talking with each other.

At first, Richards insisted he had no idea Elizabeth was only 15 until a policeman told him at the time of his arrest.

"He was lying, the whole time he was lying. The whole time, over, and over, and over, lie, lie, lie, lie, lie," Det. Robertson told Van Sant.

To see if her instincts were right, Detective Robertson asked to see Richards' Facebook page. There were literally hundreds of exchanges between him and Elizabeth.

"And I start looking at it and I realize, 'Oh, he knew, he knew before he ever came over here she was 15,'" Det. Robertson remembered.

Inside the interrogation room: "I'm in love with her"

"I looked right at him and I said … 'So are you gonna tell me the truth now?"

Det. Robertson: Wanna tell me the truth now?

Jason Richards: I fell in love with her. And I didn't know what to do.

Det. Robertson: And she told you that she was 15 and still in school?

Jason Richards: Eventually.

Det. Robertson: Right.

Elizabeth told her parents she was going jogging, but instead came to a parking lot near her house.

"This is our first meeting spot," Elizabeth told Van Sant at the lot.

"When you actually saw him face-to-face, what did you think?" he asked.

"'Holy crap,' like, I think it became a reality to me that it's not just somebody that I'm talking to over the Internet!" she replied.

Elizabeth Syrotchen and Jason Richards

Elizabeth says Jason took her to a hotel, got down on one knee and proposed marriage -- and then they got in bed. In the following weeks, he came to town again.

"On those visits you did have sex with him each time?" Van Sant asked.

"Yeah, we did," Elizabeth replied.

"For you, Jason is what?" Van Sant asked Det. Robertson.

"He's a sexual predator," she replied.

Jason Richards: I've completely just f----d up my life.

"My life was destroyed," said Elizabeth.

The events of that chaotic day still seem to haunt the Syrotchens, too.

"This hits you right now like a punch across the face," Van Sant commented to Branden.

"It's just absolutely unbelievable," he replied in tears.

"This guy found out that she was a minor and that's --and then after that's when he decided to sleep with her," Branden continued.

Richards pleaded guilty to child rape and communication with a minor for immoral purposes. His lawyer argued Richards has autism, which can be a mitigating factor for several crimes in Washington State. He got a light sentence: three years.

"When you learned that Jason was in jail?" Van San

"It broke me," Elizabeth told Van Sant.

Inexperienced at love, Elizabeth says her online connection with Jason had been instant.

"Everything progresses faster online because you're just more comfortable," she explained. "...you don't have to talk to that person in person."

District Attorney Pamela Casey says far too many internet predators are turning to apps like Kik, and their alleged crimes are making headlines across the U.S.—more crimes than Facebook and Instagram users combined.

Back in Spokane, Van Sant asked Elizabeth, "Did you fall in love with Jason?"

"Yeah, I did," she replied. "I hate to say it, but part of me still loves him."

Jason Richards

But Elizabeth didn't really have the whole story about Jason Richards. In fact, she may not have been his one true love. On Richards' phone, Det. Robertson had discovered graphic photos of young women and men.

"What's your reaction to all that?" Van Sant asked Elizabeth.

Stunned, and in tears, she stood up and left the interview room. About 10 minutes later, she returned.

"Do you want to say anything?" Van Sant asked Elizabeth.

"I just feel so fooled. Like, for three years I've been defending him and it's not right, it's not right," she replied.

Seeing some of Jason's graphic photo collection for herself drives home the point.

"That's a lot of pictures though, of a lot of different women …oh…and a man," she said looking at the photos on a computer. "Honestly, if anything, it makes me feel better. …It's going to be easier for me to move on."

Looking back, Elizabeth's mother, Brandy Syrotchen, says she wishes the judge had given Jason Richards as much as life in prison.

But back in Virginia, Nicole Lovell's mother says there is no punishment severe enough for the accused predators.

"I want both of 'em to suffer," said Tammy Weeks.

And she says Eisenhauer and Keepers aren't the only ones who should have to answer for her daughter's murder. She blames Kik, too.

"They need to shut Kik down," she said. "It's just disgusting."

Kik is now a billion-dollar company and the CEO declined "48 Hours"'request for an on-camera interview.

"It's ironic when the head of a social media company won't talk to us, so we're heading off to a technology conference in Brooklyn, New York, in hopes of catching up, with the CEO of Kik," said Van Sant.

SECRECY AND SAFETY

Evidence suggests Nicole Lovell was lured to her death over the Kik chat app – one of the same apps Elizabeth Syrotchen used to communicate with the man who almost lured her away.

As Kik's CEO Ted Livingston left the stage at the conference, "48 Hours" found him … on his smartphone.

"Mr. Livingston, Peter Van Sant, how are you?" Van Sant said. "With CBS News … I just want to ask you a quick question … What personal responsibility do you have to make sure that children are safe who use the Kik app?"

"Like, when we heard about that case, that hit the office. That hit me super hard, like, it's just, like, hard to hear about something and I grew up with a brother with disabilities..." said Livingston.

"I think it's no different than Facebook or Snapchat or Instagram. You know, you have bad people going -- " he said.

"As a parent, I disagree. I can check my child's Facebook account and Twitter account, I friend them. But with Kik I can't," Van Sant pointed out.

"Yeah, I think that's no different than Instagram. You have a private mode. You can have private messaging, all that exists there," Livingston replied.

That's true, but Kik's design is attracting millions of teens, in part, because many believe its parentproof -- the best app to keep their social lives secret.

Sadly, predators also can keep secrets on Kik.

"Kids are going to use a messenger. If we were to shut down Kik tomorrow, there'll be 10 right behind it," said Livingston.

Back in Spokane, Elizabeth Syrotchen is still struggling to make sense of what happened to her. Things with her parents are still tough … mostly because, at 18, she met a new boyfriend at the gym. He was 35.

"Would I like to see some things change? Of course," said Brandy Syrotchen.

"We'd all love to see that," Branden Syrotchen added.

"You have to compromise. You can't just be your way or the highway," Elizabeth told her father on camera.

Jason Richards got out of prison in May, and the case against him is closed. But in Blacksburg, Virginia, Nicole Lovell's murder case has yet to be resolved.

At a joint hearing for David Eisenhauer and Natalie Keepers, no cameras were allowed inside as police presented new details of Nicole's murder -- details they say were provided by Keepers herself.

News report:Investigators testified Eisenhauer covered Lovell's mouth and cut her throat. Keepers later helped Eisenhauer load Lovell's body into his car, leaving a trail of blood in the snow.

A detective testified that Keepers admitted to helping Eisenhauer plan the murder and then dispose of Nicole's body. And that Keepers was excited to be part of something secretive.

It's all too much for Nicole's mom, Tammy Weeks, who comes to court, but can't force herself to sit through the day.

"I didn't know he had stripped her naked and poured bleach on her," she said.

There is no evidence that Nicole was sexually assaulted, though Eisenhauer is formally charged with first-degree murder and abduction -- Keepers as an accessory to murder. Both also are charged with transporting or concealing a dead body. Eisenhauer has reportedly told investigators, "I believe the truth can set me free."

"Is there any doubt who is responsible for the death of your daughter?" Van Sant asked David Lovell, Nicole's father.

"No," he declared.

Eisenhauer's former internet buddy, Bryce Dustin, doesn't have much doubt either, especially after a final exchange he had with Eisenhauer around the time Nicole disappeared.

"I without a doubt believe that he did it," said Dustin.

"He texted me and said, you know, 'The original plan's failed.' And he was like, he's like, 'Do you know where I can hide a body?'" Dustin continued.

At the time, Dustin thought Eisenhauer was kidding. He, along with so many in the shell-shocked community of Blacksburg, still want to know how two intelligent college kids with their lives in front of them might wind up involved in taking the life of a 13-year-old girl.

"I wish he would've done it to me instead of her," Weeks cried. "I would trade places with her in a heartbeat. 'Cause she deserved to live."

Nicole Lovell's family: Be your kids' eyes and ears

Nicole Lovell's death is a dark reminder of how social media has profoundly changed society.

"I hope … everybody learns from this. Hold their kids tight. 'Cause it can happen to you," said Weeks.

Today, our children have a host of new ways to live… and new ways to die as well.

David Eisenhauer is scheduled to be tried in November 2017. Natalie Keepers is scheduled to be tried in February 2018 .